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  1. #1
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Posts
    82

    Default First scraping project

    I'm keen to learn how to do some basic scraping so have been reading lots, watching a few Youtube videos and on the weekend made my first scraper using a Sandvik carbide blade and some scrap. I don't expect to ever be doing full rebuilds on machines, but with having a couple of older machines the skills to even do a "rough" freshen up of a badly worn feature would be useful.

    Here's the scraper:
    IMG_3810 (Medium).JPG IMG_3811 (Medium).JPG
    The family are funding a 600x400 granite surface plate for Christmas. Its purchased sitting in my workshop as its too heavy to go under the tree - but I'm not allowed to play with it yet

    For a first project I'm thinking about making a couple of small straightedges, and stumbled across some cast iron drain grates that look like they might a good source of stock to make them. The bars on them are close to 40mm in size.
    Thinking I could cut one up to make a couple of blanks, mill them as flat/square as I can and go from there.

    Any thoughts from those with experience in this area? Good idea or am I better off starting with something else?

    IMG_3822 (Medium).JPG

    Steve

  2. #2
    Join Date
    Oct 2011
    Location
    Burnie/ Adelaide
    Age
    53
    Posts
    4,588

    Default

    I would not go the grate way as you don't know how good that cast iron is underneath. If you send a message to PDW last time I spoke to him he had some straight edge castings - he may still have something of use to you.

    Michael

  3. #3
    Join Date
    Aug 2010
    Location
    Near Bendigo, Victoria, AUS
    Age
    66
    Posts
    2,574

    Default

    I'll go along with Michael.
    On the other hand, I've used 'dubious' cast iron for a number of reasonably high precision projects....
    One thing you will need to do, no matter what you use parts of your grates for, after cutting and milling, you will almost certainly have to stress relieve the smi-finished articles. The shape of the grills means that there are lots of internal stresses from cooling very unevenly, and they will result in things warping in unexpected ways.
    I have successfully stress relieved bits by putting them in our fireplace, stoking it up pretty good to get a nice even bright orange colour throughout the parts and keeping them at that temperature for a couple of hours. Then let the fire die down and go out overnight, retrieving the parts from the ashes the next day.
    After final machining or grinding, even scraping, the cast iron parts have stayed very straight - so far.
    Josh (on this forum) and I have used an old tractor weight to make some precision ground squares as well, which were stress relieved and heat treated. That one would have been a very 'dubious' source for cast iron....
    Oh, and if it doesn't work, or your grates are full of sand or inclusions or porosity, you will have learnt something very useful in any case.
    Cheers, Joe
    again completely retired - more time to contemplate projects and spend more shed time....

  4. #4
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Posts
    82

    Default

    Thanks guys. I'll message PDW to see what he's got.
    Good point about the stress relief Joe. Obvious now you mention it but I hadn't thought about it. A month ago I could have just thrown it in the bonfire, but that option is out now until after summer. My best bet might be to fire up my shed heater and then bury it in sand to cool down once its been glowing for a while.

    I found a broken piece of the grating and cut the end off just to see what it was like inside. No sign of any sand/inclusions and having a quick play with the scraper it feels OK to work with.
    I know that's only one small sample slice, but hopefully good enough to build some skills and something useful.

    Steve

  5. #5
    Join Date
    Oct 2007
    Location
    Sydney
    Posts
    3,102

    Default

    Cast iron is available from any large metal retailer. You may need to order it however

  6. #6
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Posts
    82

    Default

    While I'm waiting on some proper straightedge castings I've been progressing with making a couple of parallels from the grating for practice.
    Got them roughed out on the mill (which also required making an arbour for the new facemill I bought a while back), and then fired up the shed heater one cooler evening over Christmas.
    Managed to get everything glowing nicely then shut the damper and left them in there until the morning to cool down:

    IMG_3868 (Medium).JPG

    Steve

  7. #7
    Join Date
    Oct 2007
    Location
    Sydney
    Posts
    3,102

    Default

    The Sandvik blanks are very good quality carbide, and come honed and polished on the faces. They are an excellent choice. However they do not have the appropriate radius on the cutting edge for push scraping. The scraper as it's shown would not scrape material correctly.

    A rule of thumb is approximately 90 mm radius for roughing, and around 60 mm for finishing. To that radius, and for cast iron, you will need to hone an 85 degree bevel to it, so you will have two distinct edges and a line in the middle where they meet. Here is a picture of 3 pf mine, and hopefully if you look at them closely you will see what I mean.

    Scrapers.jpg

  8. #8
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Posts
    82

    Default

    Thanks Pete. I've currently got about a 60mm radius on mine, and have made up a cheap bench grinder with a 180 grit diamond cup wheel and a 3000 grit honing plate to sharpen them. I've got a temporary 5deg rest set up on each end to get the correct angle.
    For anyone thinking about doing similar and starting with a Ozito grinder - don't. Buy yourself a half decent used 6" bench grinder which will have a shaft with more than 1mm step on the shaft to butt your mounting flanges to.
    IMG_3909 (Medium).JPG

    Comparison of partially scraped to how they came out of the fire:
    IMG_3907 (Medium).JPG

    Latest print (getting there....):
    IMG_3908 (Medium).JPG

    Steve

  9. #9
    Join Date
    Oct 2007
    Location
    Sydney
    Posts
    3,102

    Default

    Cool, that looks good Steve. The scraper blade you showed in the first photo was as they're sold, which is with no radius and a 90 degree hone. The diamond wheel won't get used often, pretty much only when you're initially shaping the blank and when you need a "special" to get into tight spots. The lap you will be using often however and you'll certainly notice the difference between when the blade is sharp and when it needs touching up. For some bizarre reason, the Biax doesn't dull like the hand scraper does. I have no idea why not as I would have thought it would be the other way around.

    I intended to do some scraping today as it was too hot to be outside. Instead I went for complete woosie mode and hid inside with the curtains drawn, a/c max, playing chess while whining about the weather to anyone within earshot It was a stinker!

  10. #10
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Posts
    82

    Default

    Yes, the first photo was with the carbide blank straight out of the box. I did try having a bit of a scrape with it and while it cut well, it was VERY easy to dig in a corner and make a mess. The 5deg less and smaller radius makes it much more controllable. To take a bit of the guesswork out of making the radius, I drilled a small hole in the scraper holder just behind the clamp (pretty close to 60mm from the blade edge). I poked a scriber through the hole into the MDF toolrest on the grinder and simply pivoted the handle around to make the radius. Worked well. No need to do it when using the lap as you just follow the existing edge.

    We had the hot weather yesterday. Was 45degC in the shed, but the carport had some airflow and gave me some shade so I spent the day welding and grinding making my new welding table!!

    Steve

  11. #11
    Join Date
    Mar 2017
    Location
    Brisbane
    Posts
    168

    Default

    I'm going to scrape one of my dumbell plates for practice. Need to mill it flat first of course.

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